Nitric acid oxidation processes

ABSTRACT

A process utilizing nitric acid and oxygen as co-oxidants to oxidize aldehydes, alcohols, polyols, preferably carbohydrates, specifically reducing sugars to produce the corresponding carboxylic acids.

RELATED APPLICATION INFORMATION

This claims priority to U.S. Patent Application No. 61/780,472, filed onMar. 13, 2013, and U.S. Patent Application No. 61/780,498, filed on Mar.13, 2013, the entire contents of all of which are fully incorporatedherein by reference.

FIELD OF THE INVENTION

This invention describes improved processes utilizing nitric acid andoxygen as co-oxidants to oxidize aldehydes, alcohols and/or polyols,preferably carbohydrates to produce the corresponding carboxylic acids.The improved processes described herein can be used as a batch processor as a continuous process.

BACKGROUND OF THE INVENTION

Hydroxycarboxylic acids, and in particular carbohydrate diacids (aldaricacids) offer significant economic potential as carbon based chemicalbuilding blocks for the chemical industry, as safe additives orcomponents of products used in pharmaceutical preparations and foodproducts, and as structural components of biodegradable polymers, ifthey can be effectively produced on an industrial scale. Glucaric acid,for example, is produced through the oxidation of glucose and in saltform is currently in use as a nutraceutical for preventing cancer. Theprice of this material however is high, approximately $100/lb.Industrial scale production of aldaric acids would also providesufficient materials for the production of other useful compounds, thatinclude environmentally degradable polyamides with varying propertiesand applications, which are otherwise not commercially available.

Carbohydrate diacids are produced a number of ways from reducing sugarsusing a variety of oxidizing agents, including nitric acid. An exampleof a nitric acid oxidation of a carbohydrate is that of D-glucose togive D-glucaric acid, typically isolated as its mono potassium salt(See, W. N. Haworth and W. G. M. Jones, J. Chem. Soc., 65-76 (1944), C.L. Mehltretter and C. E. Rist, Agric. and Food Chem., 1, 779-783 (1953)and C. L. Mehltretter, “D-Glucaric Acid”, in Methods in CarbohydrateChemistry, R. L. Whistler, M. L. Wolfrom, Eds; Academic Press, New York,1962, Vol. II, pp 46-48). Alternatively, D-glucaric acid can be isolatedfrom nitric acid oxidation of D-glucose as a disodium salt (See, D. E.Kiely, A. Carter and D. P. Shrout, U.S. Pat. No. 5,599,977, Feb. 4,1997) or as the 1,4:6,3-dilactone (See, D. E. Kiely and G. Ponder, U.S.Pat. No. 6,049,004, Apr. 11, 2000). Routes have been described showingsynthesis of diacids through catalytic oxidation with oxygen over anoble metal catalyst (See, C. L. Mehltretter, U.S. Pat. No. 2,472,168,Jun. 7, 1949). An additional route of synthesis exists by use ofoxoammonium salts in combination with hypophalites as the terminaloxidants. For example, Merbough and coworkers describe oxidation ofD-glucose, D-mannose and D-galactose to their corresponding diacidsusing 4-acetylamino-2,2,4,6-tetamethyl-1-piperidinyloxy (4-AcNH-TEMPO)with hypohalites as the oxidizing medium (See, N. Merbough, J. M.Bobbitt and C. Bruckner, J. Carbohydr. Chem., 21, 66-77 (2002) andMerbouh, J M. Bobbitt, and C. Bruckner, U.S. Pat. No. 6,498,269, Dec.24, 2002). A microbial oxidation of myo-inositol to glucuronic acidwhich is then oxidized enzymatically or by catalytic oxidation toglucaric acid has also been recently described (See, W. A. Schroeder, P.M. Hicks, S. McFarlan, and T. W. Abraham, U.S. Patent Application,20040185562, Sep. 24, 2004).

A variety of different processes for the oxidation of carbohydratesusing nitric acid are known. For example, U.S. Pat. No. 2,380,196 (the'196 patent) describes the nitric acid oxidation of carbohydrates todibasic acids, particularly tartaric acid. The '196 patent describes acyclic process in which in each cycle, fresh carbohydrate and residuefrom a previous oxidation is oxidized with nitric acid. A catalyst, suchas vanadium, manganese, iron and molybdenum, is employed to increase theyield of tartaric acid. According to the '196 patent, good yields areobtained when the molar ratio of nitric acid to glucose is 5:7.5,preferably 6:7.5. The '196 patent also describes that when mixing theingredients, the temperature should be maintained at 20° C. or lower.Following mixing, the temperature is raised gradually or allowed to risespontaneously to about 30° C. to 35° C. (this is the induction orheating-up stage). When the temperature reaches 30° C. to 35° C., anautocatalytic strong exothermic reaction called the “blow” sets in. The“blow” stage is maintained at a temperature of about 50° C. to 75° C.,preferably 65-70° C. for anywhere from 45 to 120 minutes. The finaltemperature stage of the oxidation is the “fume-off” stage at which thelast of the nitric acid is reacted and passed off as lower nitrogenoxides. During the “fume-off” stage, the reaction mixture is maintainedat a high temperature somewhat below the boiling point of the mixture,at approximately 90° C. to 95° C. until nitrogen oxide is no longerdetectable by the fumes. Oxalic and tartaric acids are recovered fromthe oxidized reaction mixture by direct precipitation andcrystallization.

U.S. Pat. No. 2,436,659 (the '659 patent) discloses an improved andeconomical process for the production of D-saccharic acid. Specifically,the '659 patent discloses a process that produces higher yields ofD-saccharic acid in a shorter period of time, is more convenient whilenot employing the use of metal oxidation catalysts. According to the'659 patent, crystalline D-glucose, in anhydrous or monohydrate form, isadded to a solution of nitric acid at a rate that allows control of thetemperature of the reaction between 55° C. to 90° C. The mole ratio ofglucose to nitric acid used in the process is 1:4. However, the '659patent notes that a mole ratio of glucose to nitric acid of 1:3 lowersthe yield of D-saccharic acid while a ratio of 1:8 increases this yield.The '659 patent also discloses that when 60 to 70 percent nitric acid isused it is preferred to use reaction temperatures of 55° C. to 70° C.and that when lower concentrations of nitric acid are employed higherreaction temperatures are preferred. When the process is performed inthis manner, it is quite rapid, with maximum yields of D-saccharic acidbeing obtained in a one-hour period of oxidation.

U.S. Pat. No. 3,242,207 (the '207 patent) discloses a continuous processfor the oxidation of D-glucose with nitric acid at elevatedtemperatures. Specifically, the process described in the '207 patent isperformed as follows: (1) to an initial reaction mixture prepared byoxidizing an aqueous solution of D-glucose with concentrated nitricacids, an aqueous D-glucose solution and concentrated nitric acid in themolecular ratio of 1:3 to 1:3.5 is simultaneously and continuously addedat a temperature of about 40° C. to 70° C.; (2) continuously withdrawingfrom the reaction vessel an apportion of the reaction mixturecorresponding to the volume of the fed-in liquids; and (3) isolating theproduct formed.

U.S. Pat. No. 7,692,041 (the '041 patent) discloses an improved methodfor oxidizing water soluble compounds using nitric acid oxidation. Themethod involves (1) preparing an aqueous solution of an organic compoundsuitable for nitric acid oxidation; (2) combining, over time, employinga controlled process, in a closed reaction vessel, under positivepressure of oxygen, the aqueous solution of the organic compound and anaqueous solution of nitric acid to oxidize the organic compound to amixture of organic acids; (3) maintaining controlled, moderatetemperatures of from about 25° C. to about 50° C., controlled positivepressure of oxygen, and controlled agitation of the organic compound andnitric acid reaction mixture during the oxidation reaction; and (4)removing a portion of the nitric acid from the combined aqueous solutionto give a mixture of organic acids suitable for further processing.

There is a need in the art for improved oxidation process that is safe,economical and efficient for converting organic compounds into theircorresponding acids.

SUMMARY OF THE INVENTION

In one aspect, the present invention relates to a method of synthesizinga mixture of organic acids, the method comprising the steps of:

(a) combining, over time, in one or more closed reaction vessels, undera positive pressure of oxygen and with continuous mixing, an organiccompound suitable for nitric acid oxidation and an aqueous solution ofnitric acid to form a first reaction mixture, wherein the organiccompound and the aqueous solution of nitric acid are introduced into theone or more closed reaction vessels;

(b) flowing said first reaction mixture through the one or more reactionvessels while maintaining a controlled temperature of from about 5° C.to about 105° C. and controlled positive pressure of oxygen of fromabout 0 barg to about 1000 barg for a time period suitable to oxidizethe organic compound to a subsequent reaction mixture comprising amixture of organic acid products and nitrogen oxides;

(c) recirculating the subsequent reaction mixture into the reactionvessel vapor space headspace; and

(d) recovering nitric acid from the subsequent reaction mixture.

In the above method, the one or more closed reaction vessels compriseone or more reactors. More specifically, the one or more closed reactionvessels are in series (continuous) or in parallel with one another(batch). For example, the reactor can be a continuously stirred tankreactor (CSTRs), falling film reactors or tubular type plug flow reactoralmost any type reactor that mixes, controls temperature and pressureand has a liquid and gas phase (not hydraulically full).

The above method can be a continuous process. Alternatively, the abovemethod can be a batch process.

In the above method, the organic compound comprises a single organicmaterial or a mixture of organic materials suitable for nitric acidoxidation.

In another aspect, the above method further comprises the step ofremoving a significant portion of the nitric acid from the subsequentreaction mixture.

In the above method, the removal of the nitric acid is accomplished byan evaporation, distillation, nanofiltration, diffusion dialysis oralcohol or ether precipitation.

The above method further comprises the step of making basic thesubsequent reaction mixture from which most of the nitric acid has beenremoved to convert residual nitric acid to inorganic nitrate and themixture of organic acids to a mixture of organic acid salts.

In the above method, organic compound suitable for nitric acid oxidationis selected from the group consisting of monohydric alcohols, diols,polyols, aldehydes, ketones, carbohydrates, hydroxyacids, cellulose,starch and combinations thereof. For example, the carbohydrates areselected from the group consisting of monosaccharides, disaccharides,oligosaccharides, aldonic acids, aldonic acid esters, aldonic acidsalts, aluronic acids, alduronic acid esters, alduronic acid salts,alditols, cyclitols, corn syrups with different dextrose equivalentvalues, and monosaccharides, disaccharides, oligosaccharides andpolysaccharides derived from plants, microorganisms or biomass sources.

In the above method, the nitrogen oxides are N₂O₃, N₂O₄, NO, NO₂ andN₂O.

In another aspect, the present invention relates to a method ofsynthesizing a mixture of organic acids, the method comprising the stepsof:

(a) combining, over time, in one or more closed reaction vessels, undera positive pressure of oxygen and with continuous stirring mixing anorganic compound suitable for nitric acid oxidation and an aqueoussolution of nitric acid to form a reaction mixture, wherein the organiccompound and the aqueous solution of nitric acid are concurrentlyintroduced into the one or more closed reaction vessels;

(b) flowing said reaction mixture through the one or more closedreaction vessels while (i) maintaining a controlled temperature of fromabout 5° C. to about 105° C. in a portion of the reaction vessel, (ii)maintaining a reaction vessel headspace temperature of from about 80° C.to about −42° C.; and (iii) a controlled positive pressure of oxygen offrom about 0 barg to about 1000 barg for a time period suitable tooxidize the organic compound to a subsequent reaction mixture comprisinga mixture of organic acid products and nitrogen oxides; and

(c) removing most of nitric acid from the subsequent reaction mixture togive a final reaction mixture of organic acids suitable for furtherprocessing.

In the above method, the one or more closed reaction vessels compriseone or more reactors. More specifically, the one or more closed reactionvessels are in series (continuous) or in parallel with one another(batch). For example, the reactor can be a continuously stirred tankreactor (CSTRs), falling film reactor or a tubular type plug flowreactor or almost any type reactor that can mix, controls temperatureand pressure and has a liquid and gas phase (not hydraulicly full). Theabove method can be a continuous process. Alternatively, the abovemethod can be a batch process.

In the above method, the organic compound comprises a single organicmaterial or a mixture of organic materials suitable for nitric acidoxidation.

In another aspect, the above method further comprises the step ofremoving a significant portion of the nitric acid from the subsequentreaction mixture.

In the above method, the removal of the nitric acid is accomplished byan evaporation, distillation, nanofiltration, diffusion dialysis oralcohol or ether precipitation.

The above method further comprises the step of making basic thesubsequent reaction mixture from which most of the nitric acid has beenremoved to convert residual nitric acid to inorganic nitrate and themixture of organic acids to a mixture of organic acid salts.

In the above method, organic compound suitable for nitric acid oxidationis selected from the group consisting of monohydric alcohols, diols,polyols, aldehydes, ketones, carbohydrates, hydroxyacids, cellulose,starch and combinations thereof. For example, the carbohydrates areselected from the group consisting of monosaccharides, disaccharides,oligosaccharides, aldonic acids, aldonic acid esters, aldonic acidsalts, aluronic acids, alduronic acid esters, alduronic acid salts,alditols, cyclitols, corn syrups with different dextrose equivalentvalues, and monosaccharides, disaccharides, oligosaccharides andpolysaccharides derived from plants, microorganisms or biomass sources.

In the above method, the nitrogen oxides are N₂O₃, N₂O₄, NO, NO₂ andN₂O.

BRIEF DESCRIPTION OF THE FIGURE

FIG. 1 provides the results described in Example 11 demonstrating alower NO₂ composition in the headspace of a reactor equipped withheadspace cooling compared to that of an identical reactor not equippedwith headspace cooling.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a safe, efficient and economicaloxidation process for oxidizing organic compounds into theircorresponding organic acid products. Specifically, this inventionrelates to an improved method for regenerating nitric acid in situduring the oxidation reaction while also improving the safety andquality of the final product. Effective regeneration of nitric acidreduces the amount of nitric acid required to accomplish the oxidationand allows subsequent recovery and recycling of the nitric acid thusimproving the efficiency and economy of the process. However, increasingthe amount of nitric acid during the reaction can also lead to run awayoxidation rates and over oxidation of the organic substrate. Otherpatents have disclosed methods for regenerating nitric acid in situduring the oxidation process. U.S. Pat. No. 7,692,041 (the '041 patent)discloses an improved method for oxidizing water soluble compounds usingnitric acid oxidation whereby a positive pressure of oxygen isintroduced during the reaction to convert gaseous oxides of nitrogen(NOx), by-products from the oxidation, back to nitric acid. The processdescribed in the '041 patent uses a sealed vessel, pressurized withoxygen to re-oxidize NOx in the headspace back to nitric acid, therebyimproving reaction rates by increasing the nitric acid concentration inthe liquid reaction phase. The '041 patent does not describe alternativemethods of improving nitric acid regeneration or oxidation reactionrates. One skilled in the art would expect that increasing thetemperature in the headspace would improve nitric acid regeneration byincreasing the oxidation rate of NOx back to nitric acid. One skilled inthe art would also expect that improving mass transfer of the gas phaseback into the liquid phase would increase oxidation rates of the organicsubstrate.

To better understand the effects of headspace temperature, the inventorsused a reactor capable of independently heating and cooling gas andliquid. The '041 patent does not disclose using a reactor having aseparate control over headspace and liquid temperatures. Surprisingly,the inventors found that cooling, instead of heating, the headspacebelow the temperature of the liquid phase improved the overall rate ofnitric acid regeneration. Increasing the rate of nitric acidregeneration allows the oxidation process of this invention to use lessnitric acid than previously described to achieve the same degree ofoxidation.

Additionally, in another aspect, while trying to improve nitric acidregeneration by increasing mass transfer of the gas phase into theliquid phase by recirculating the liquid reaction mixture into thegaseous headspace, the inventors surprisingly discovered that theoxidation reaction rates did not increase and in fact, the oxidation wasquenched and conversion of the organic substrate into organic acidproducts was stopped. This surprising result may be used to control theenergetic oxidation reaction, particularly in preventing over oxidationof the organic substrate once the desired level of oxidation has beenreached. This is particularly effective when combined with improvednitric acid regeneration through cooling of the headspace which leads tofaster oxidation rates and makes control over the degree of oxidationdifficult to control.

The oxidation process described herein can be performed as a batch-typeprocess or as a continuous process. The first step of the process of thepresent invention involves combining an organic compound suitable fornitric acid oxidation with an aqueous solution of nitric acid to form aninitial or first reaction mixture, whereby the organic compound isoxidized to form a reaction mixture of organic acids (which constitutepart of the liquid phase during the reaction). It should also be notedthat during the oxidation that gaseous oxides of nitrogen (gaseousoxides of nitrogen are also referred to herein as “nitrogen oxides” andinclude N₂O₃, N₂O₄, NO, NO₂ and N₂O) are produced in the reactionmixture (which constitute part of the gas or gaseous phase). In oneaspect, the organic compound and aqueous solution of nitric acid can beinjected simultaneously or sequentially, in any order, into one or moreclosed reaction vessels that comprise a reaction vessel train.

The organic compounds that can be used in the process of the presentinvention can generally be described to include monohydric alcohols,diols, polyols, aldehydes, ketones, carbohydrates, and mixtures thereof.Non-limiting examples of carbohydrates that may be used in the processesof the current invention include, but are not limited to,monosaccharides, such as the common monosaccharides D-glucose,D-mannose, D-xylose, L-arabinose, D-arabinose, D-galactose, D-arabinose,D-ribose, D-fructose; disaccharides, such as the common disaccharidesmaltose, sucrose, isomaltose, cellobiose and lactose; oligosaccharides,for example, maltotriose and maltotetrose; aldonic acids such asD-gluconic acid, D-ribonic acid, and D-galactonic acid; aldonic acidesters, lactones and salts that include, but are not limited to, thosederived from D-gluconic acid, D-ribonic acid and D-galactonic acid;alduronic acids, for example, D-glucuronic acid and L-iduronic acid;alduronic esters, lactones and salts that include, but are not limitedto, those derived from D-glucuronic acid and L-iduronic acid; alditolsthat include glycerol, threitol, erythritol, xylitol, D-glucitol;alditols with more than six carbon atoms; cyclitols, for example commoncyclitols such as myo-inositol and scyllitol; corn syrups with differentdextrose equivalent values; other aldonic acids and salts thereof, suchas, glucoheptonic acids, glycerbionic acids, erythrobionic acids,threobionic acids, ribobionic acids, arabinobionic acids, xylobionicacids, lyxobionic acids, allobionic acids, altrobionic acids,glucobionic acids, mannobionic acids, gulobionic acids, idobionic acids,galactobionic acids, talobionic acids, alloheptobionic acids,altroheptobionic acids, glucoheptobionic acids, mannoheptobionic acids,guloheptobionic acids, idoheptobionic acids, galactoheptobionic acidsand taloheptobionic acids; glycols such as ethylene glycol, diethyleneglycols, triethylene glycols or mixtures thereof; mixtures ofcarbohydrates from different biomass, plant or microorganism sources;polysaccharides from biomass, plant or microorganism sources (such asstarch, celluloses, etc.) and of varying structures, saccharide unitsand molecular weights. The organic compound may also comprise acombination of one or more of the organic compounds. The organiccompound may be added neat (namely, as pure substance as a solid orliquid (namely, aqueous)), depending on the desired properties of thereaction mixture. In one aspect, the organic compound is provided as anaqueous solution.

As mentioned previously herein, the organic compound is combined with anaqueous solution of nitric acid to form the initial or first reactionmixture. The concentration of nitric acid used in the process of thepresent invention is not critical. For example, the nitric acid used canbe 60% nitric acid, 70% nitric acid, etc. It will be understood by oneskilled in the art that the ratio of aqueous nitric acid to organiccompound used in the process of the present invention can vary dependingon the desired oxidation product composition. The molar ratio iscalculated at the beginning of the reaction if all reactants are addedat the beginning of the reaction in batch (all together) or in acontinuous flow reactor system (all together in the first reactor of thereactor system). The molar ratio is calculated at the end of thereaction step if a fed batch is used (the phrase “fed batch” meansstarting with one of the reactants (such as an organic compound ornitric acid) in a reaction vessel and then adding the other reactants asthe reaction progresses to completion) or if a continuous series ofreaction vessels are used and one of the reactants is added at differentlocations through the reactor train (an amount is added to each reactorvessel in the reactor train). In one aspect, the molar ratio of aqueousnitric acid to organic compound ranges from approximately 0.1:1 toapproximately 2:1. In yet another aspect, the molar ratio of aqueousnitric acid to organic compound ranges from approximately 0.25:1 toapproximately 1.8:1. In still yet another aspect, the molar ratio ofaqueous nitric acid to organic compound ranges from approximately 0.25:1to approximately 1.7:1. In still yet another aspect, the molar ratio ofaqueous nitric acid to organic compound ranges from approximately 0.25:1to approximately 1.6:1. In still yet another aspect, the molar ratio ofaqueous nitric acid to organic compound ranges from approximately 0.25:1to approximately 1.5:1. In yet another aspect, the molar ratio ofaqueous nitric acid to organic compound ranges from approximately 0.25:1to approximately 1.4:1. In yet another aspect, the molar ratio ofaqueous nitric acid to organic compound ranges from approximately 0.25:1to approximately 1.3:1. In yet another aspect, the molar ratio ofaqueous nitric acid to organic compound ranges from approximately 0.25:1to approximately 1.2:1. In yet another aspect, the molar ratio ofaqueous nitric acid to organic compound ranges from approximately 0.25:1to approximately 1:1. In yet another aspect, the molar ratio of aqueousnitric acid to organic compound is approximately 0.25:1 to approximately0.9:1. In yet another aspect, the molar ratio of aqueous nitric acid toorganic compound is approximately 0.25:1 to approximately 0.8:1. In yetanother aspect, the molar ratio of aqueous nitric acid to organiccompound is approximately 0.25:1 to approximately 0.75:1. In yet anotheraspect, the molar ratio of aqueous nitric acid to organic compound isapproximately 0.25:1 to approximately 0.65:1. In yet another aspect, themolar ratio of aqueous nitric acid to organic compound ranges fromapproximately 0.4:1 to approximately 1.8:1. In yet another aspect, themolar ratio of aqueous nitric acid to organic compound ranges fromapproximately 0.4:1 to approximately 1.7:1. In yet another aspect, themolar ratio of aqueous nitric acid to organic compound ranges fromapproximately 0.4:1 to approximately 1.6:1. In yet another aspect, themolar ratio of aqueous nitric acid to organic compound ranges fromapproximately 0.4:1 to approximately 1.5:1. In yet another aspect, themolar ratio of aqueous nitric acid to organic compound ranges fromapproximately 0.4:1 to approximately 1.4:1. In yet another aspect, themolar ratio of aqueous nitric acid to organic compound ranges fromapproximately 0.4:1 to approximately 1.3:1. In yet another aspect, themolar ratio of aqueous nitric acid to organic compound ranges fromapproximately 0.4:1 to approximately 1.2:1. In yet another aspect, themolar ratio of aqueous nitric acid to organic compound ranges fromapproximately 0.4:1 to approximately 1:1. In another aspect, the molarratio of aqueous nitric acid to organic compound is approximately 0.4:1to approximately 0.9:1. In another aspect, the molar ratio of aqueousnitric acid to organic compound is approximately 0.4:1 to approximately0.8:1. In another aspect, the molar ratio of aqueous nitric acid toorganic compound is approximately 0.4:1 to approximately 0.75:1. Inanother aspect, the molar ratio of aqueous nitric acid to organiccompound is approximately 0.4:1 to approximately 0.65:1. In yet anotheraspect, the molar ratio of aqueous nitric acid to organic compoundranges from approximately 0.5:1 to approximately 1.8:1. In yet anotheraspect, the molar ratio of aqueous nitric acid to organic compoundranges from approximately 0.5:1 to approximately 1.7:1. In yet anotheraspect, the molar ratio of aqueous nitric acid to organic compoundranges from approximately 0.5:1 to approximately 1.6:1. In yet anotheraspect, the molar ratio of aqueous nitric acid to organic compoundranges from approximately 0.5:1 to approximately 1.5:1. In yet anotheraspect, the molar ratio of aqueous nitric acid to organic compoundranges from approximately 0.5:1 to approximately 1.4:1. In yet anotheraspect, the molar ratio of aqueous nitric acid to organic compoundranges from approximately 0.5:1 to approximately 1.3:1. In yet anotheraspect, the molar ratio of aqueous nitric acid to organic compoundranges from approximately 0.5:1 to approximately 1.2:1. In yet anotheraspect, the molar ratio of aqueous nitric acid to organic compoundranges from approximately 0.5:1 to approximately 1:1. In another aspect,the molar ratio of aqueous nitric acid to organic compound isapproximately 0.5:1 to approximately 0.9:1. In another aspect, the molarratio of aqueous nitric acid to organic compound is approximately 0.5:1to approximately 0.8:1. In another aspect, the molar ratio of aqueousnitric acid to organic compound is approximately 0.5:1 to approximately0.75:1. In another aspect, the molar ratio of aqueous nitric acid toorganic compound is approximately 0.5:1 to approximately 0.65:1. Inanother aspect, the molar ratio of aqueous nitric acid to organiccompound is approximately 0.5:1 to approximately 0.65:1. In a furtheraspect, the molar ratio of aqueous nitric acid to organic compound isapproximately 0.5:1. In a further aspect, the molar ratio of aqueousnitric acid to organic compound is approximately 0.6:1. In a furtheraspect, the molar ratio of aqueous nitric acid to organic compound isapproximately 0.7:1. In a further aspect, the molar ratio of aqueousnitric acid to organic compound is approximately 0.8:1. In a furtheraspect, the molar ratio of aqueous nitric acid to organic compound isapproximately 0.9:1. In yet a further aspect, the molar ratio of aqueousnitric acid to organic compound is approximately 0.1:2. In still yet afurther aspect, the molar ratio of aqueous nitric acid to organiccompound is approximately 0.1:1.5. In still yet a further aspect, themolar ratio of aqueous nitric acid to organic compound is approximately0.1:1. In yet a further aspect, the molar ratio of aqueous nitric acidto organic compound is approximately 0.25:3. In still yet a furtheraspect, the molar ratio of aqueous nitric acid to organic compound isapproximately 0.25:1.5. In still yet a further aspect, the molar ratioof aqueous nitric acid to organic compound is approximately 0.25:1. Inyet a further aspect, the molar ratio of aqueous nitric acid to organiccompound is approximately 0.50:2. In still yet a further aspect, themolar ratio of aqueous nitric acid to organic compound is approximately0.50:1.5. In still yet another aspect, the molar ratio of aqueous nitricacid to organic compound is approximately 1.5:1. In still yet anotheraspect, the molar ratio of aqueous nitric acid to organic compound isapproximately 2:1.

Optionally, inorganic nitrate can be added into the reaction mixture atany time during the oxidation process. Generally, the inorganic nitritewill be added at the beginning during the period of time that the firstreaction mixture is being formed. Generally, once the oxidation reactionhas begun, it may no longer be necessary to add any additional nitrate.

The initial reaction mixture is prepared (in one or more reactionvessels) at a temperature that generally ranges from about 5° C. toabout 105° C. For example, the temperature ranges may be from about 10°C. to about 105° C., about 15° C. to about 105° C., about 20° C. toabout 105° C., about 25° C. to about 105° C., about 30° C. to about 105°C., about 35° C. to about 105° C., about 40° C. to about 105° C., about45° C. to about 105° C., about 50° C. to about 105° C., about 55° C. toabout 105° C., about 60° C. to about 105° C., about 5° C. to about 100°C., about 10° C. to about 100° C., about 15° C. to about 100° C., about20° C. to about 100° C., about 25° C. to about 100° C., about 30° C. toabout 100° C., about 35° C. to about 100° C., about 40° C. to about 100°C., about 45° C. to about 100° C., about 50° C. to about 100° C., about55° C. to about 100° C., about 60° C. to about 100° C., about 5° C. toabout 95° C., about 10° C. to about 95° C., about 15° C. to about 95°C., about 20° C. to about 95° C., about 25° C. to about 95° C., about30° C. to about 95° C., about 35° C. to about 95° C., about 40° C. toabout 95° C., about 45° C. to about 95° C., about 50° C. to about 95°C., about 55° C. to about 95° C., about 60° C. to about 95° C., about 5°C. to about 90° C., about 10° C. to about 90° C., about 15° C. to about90° C., about 20° C. to about 90° C., about 25° C. to about 90° C.,about 30° C. to about 90° C., about 35° C. to about 90° C., about 40° C.to about 90° C., about 45° C. to about 90° C., about 50° C. to about 90°C., about 55° C. to about 90° C., about 60° C. to about 90° C., about 5°C. to about 85° C., about 10° C. to about 85° C., about 15° C. to about85° C., about 20° C. to about 85° C., about 25° C. to about 85° C.,about 30° C. to about 85° C., about 35° C. to about 85° C., about 40° C.to about 85° C., about 45° C. to about 85° C., about 50° C. to about 85°C., about 55° C. to about 85° C., about 60° C. to about 85° C., about 5°C. to about 80° C., about 10° C. to about 80° C., about 15° C. to about80° C., about 20° C. to about 80° C., about 25° C. to about 80° C.,about 30° C. to about 80° C., about 35° C. to about 80° C., about 40° C.to about 80° C., about 45° C. to about 80° C., about 50° C. to about 80°C., about 55° C. to about 80° C., about 60° C. to about 80° C., about 5°C. to about 70° C., about 10° C. to about 70° C., about 15° C. to about70° C., about 20° C. to about 70° C., about 25° C. to about 70° C.,about 30° C. to about 70° C., about 35° C. to about 70° C., about 40° C.to about 70° C., about 45° C. to about 70° C., about 50° C. to about 70°C., about 55° C. to about 70° C., about 60° C. to about 70° C., about55° C. to about 105° C., about 60° C. to about 105° C., about 65° C. toabout 105° C., about 70° C. to about 105° C., about 75° C. to about 105°C., about 80° C. to about 105° C., about 85° C. to about 105° C., about90° C. to about 105° C., about 55° C. to about 100° C., about 60° C. toabout 100° C., about 65° C. to about 100° C., about 70° C. to about 100°C., about 75° C. to about 100° C., about 80° C. to about 100° C., about85° C. to about 100° C., about 90° C. to about 100° C., about 55° C. toabout 95° C., about 60° C. to about 95° C., about 65° C. to about 95°C., about 70° C. to about 95° C., about 75° C. to about 95° C., about80° C. to about 95° C., about 85° C. to about 95° C., about 90° C. toabout 95° C., about 55° C. to about 90° C., about 60° C. to about 90°C., about 65° C. to about 90° C., about 70° C. to about 90° C., about75° C. to about 90° C., about 80° C. to about 90° C., about 85° C. toabout 90° C., about 10° C. to about 55° C., about 15° C. to about 55°C., about 20° C. to about 55° C., about 25° C. to about 55° C., about10° C. to about 50° C., about 15° C. to about 50° C., about 20° C. toabout 50° C., about 25° C. to about 50° C., about 10° C. to about 45°C., about 15° C. to about 45° C., about 20° C. to about 45° C., about25° C. to about 45° C., about 10° C. to about 40° C., about 15° C. toabout 40° C., about 20° C. to about 40° C., about 25° C. to about 40°C., about 10° C. to about 35° C., about 15° C. to about 35° C., about20° C. to about 35° C., about 25° C. to about 35° C., about 10° C. toabout 30° C., about 15° C. to about 30° C., about 20° C. to about 30°C., or about 25° C. to about 30° C.

As mentioned previously, the reaction mixture is contained within one ormore closed reaction vessels that are capable of carrying out theoxidation process. For example, any type of reaction vessel that allowsfor the gas and liquid phases to have a high mass transfer during theoxidation reaction can be used. In one aspect, the reactor is capable ofindependently heating and cooling the gas and liquid phases. Examples ofreactor vessels that can be used include one or more continuouslystirred tank reactors (CSTRs), plug flow reactors, spinning discreactors, or tubular type plug flow reactors. Additionally, the reactionvessel can contain heat transfer systems such as coils, jackets, loops,etc. Furthermore, when one or more reaction vessels are used, anycombination of different types and kinds of reaction vessels can be use.For example, the reaction train can contain a combination of one or moreCSTRs, one or more tubular type plug flow reactors, and/or one or moreevaporators. The reaction train contain one reaction vessel, tworeaction vessels, three reaction vessels, four reaction vessels, fivereaction vessels, six reaction vessels, seven reaction vessels, eightreaction vessels, nine reaction vessels or ten reaction vessels. If oneor more reaction vessels are used, the reaction vessels can be connectedin series with one another or one (such as in a continuous process) orone or more reaction vessels can be used in parallel (such as in a batchprocess).

The reaction vessel can be described as a container or vessel that isinsulated from the external environment, such that the reaction mixturecontained within the tank reactor is not exposed to ambient air.Additionally, the reaction vessel can comprise one or more mixingelements that are capable of continuously stirring and providingcontrolled agitation of the reaction mixture within the vessel. The oneor more mixing elements may include, but are not limited to magneticstirrers, propeller stirrers, turbine stirrers, anchor stirrers,kneading stirrers, centrifugal stirrers, paddle stirrers andcombinations thereof. Generally, the mixing element is electronicallycontrolled such that the spinning velocity of the mixing element may bealtered as needed.

The reaction vessel typically maintains a vapor or head space whereinthe gaseous phase (gaseous oxides of nitrogen) exists in addition to theliquid phase. The vapor or head space is created by filing the tankreactor with a volume of the reaction mixture that is less than 100% ofthe volume of the tank. Generally, the reaction vessel is filled with avolume that ranges from approximately 1% of the reaction vessel volumeto approximately 99% of the reaction vessel volume. In certain aspectsof the current invention, the reaction mixture comprises a volume of thereaction vessel that is not greater than 95%, not greater than 90%, notgreater than 85%, not greater than 80%, not greater than 75%, notgreater than 70%, not greater than 65%, not greater than 60%, notgreater than 55%, not greater than 50%, not greater than 45%, notgreater than 40%, not greater than 35%, not greater than 30%, notgreater than 25%, not greater than 20%, not greater than 15%, notgreater than 10%, and not greater than 5%.

In one aspect, the vapor or head space of one or more reaction vesselsmay be maintained at a temperature of from about 80° C. to about −42° C.For example, the temperature of the vapor (gas phase) or head space canbe from about 80° C. to about −41° C., about 80° C. to about −40° C.,about 80° C. to about −35° C., about 80° C. to about −30° C., about 80°C. to about −20° C., about 80° C. to about −15° C., about 80° C. toabout −10° C., about 80° C. to about 0° C., about 80° C. to about 10°C., about 80° C. to about 20° C., about 80° C. to about 30° C., about80° C. to about 40° C., about 70° C. to about −42° C., about 70° C. toabout −41° C., about 70° C. to about −40° C., about 70° C. to about −35°C., about 70° C. to about −30° C., about 70° C. to about −20° C., about70° C. to about −15° C., about 70° C. to about −10° C., about 70° C. toabout 0° C., about 70° C. to about 10° C., about 70° C. to about 20° C.,about 70° C. to about 30° C., about 70° C. to about 40° C., about 60° C.to about −42° C., about 60° C. to about −41° C., about 60° C. to about−40° C., about 60° C. to about −35° C., about 60° C. to about −30° C.,about 60° C. to about −20° C., about 60° C. to about −15° C., about 60°C. to about −10° C., about 60° C. to about 0° C., about 60° C. to about10° C., about 60° C. to about 20° C., about 60° C. to about 60° C.,about 60° C. to about 40° C., about 50° C. to about −42° C., about 50°C. to about −41° C., about 50° C. to about −40° C., about 50° C. toabout −35° C., about 50° C. to about −30° C., about 50° C. to about −20°C., about 50° C. to about −15° C., about 50° C. to about −10° C., about50° C. to about 0° C., about 50° C. to about 10° C., about 50° C. toabout 20° C., about 50° C. to about 30° C., about 50° C. to about 40°C., about 40° C. to about −42° C., about 40° C. to about −41° C., about40° C. to about −40° C., about 40° C. to about −35° C., about 40° C. toabout −30° C., about 40° C. to about −20° C., about 40° C. to about −15°C., about 40° C. to about −10° C., about 40° C. to about 0° C., about40° C. to about 10° C., about 40° C. to about 20° C., about 40° C. toabout 30° C., about 30° C. to about −42° C., about 30° C. to about −41°C., about 30° C. to about −40° C., about 30° C. to about −35° C., about30° C. to about −30° C., about 30° C. to about −20° C., about 30° C. toabout −15° C., about 30° C. to about −10° C., about 30° C. to about 0°C., about 30° C. to about 10° C., about 30° C. to about 20° C., about20° C. to about −42° C., about 20° C. to about −41° C., about 20° C. toabout −40° C., about 20° C. to about −35° C., about 20° C. to about −30°C., about 20° C. to about −20° C., about 20° C. to about −15° C., about20° C. to about −10° C., about 20° C. to about 0° C., about 20° C. toabout 10° C., about 10° C. to about −42° C., about 10° C. to about −41°C., about 10° C. to about −40° C., about 10° C. to about −35° C., about10° C. to about −30° C., about 10° C. to about −20° C., about 10° C. toabout −15° C., about 10° C. to about −10° C., about 10° C. to about 0°C., about 5° C. to about −42° C., about 5° C. to about −41° C., about 5°C. to about −40° C., about 5° C. to about −35° C., about 5° C. to about−30° C., about 5° C. to about −20° C., about 5° C. to about −15° C.,about 5° C. to about −10° C. or about 5° C. to about 0° C. While thevapor or head space of one or more reaction vessels may be maintained ata temperature of from about 80° C. to about −42° C., the liquid phase ofthe one or more reaction vessels may be maintained at a temperature of5° C. to about 105° C. In one aspect, the vapor or head space ismaintained at a lower temperature than the temperature of the liquidphase in the reaction vessel. For example, the vapor or head space is atleast 1° C., 5° C., 10° C., 15° C., 20° C., 25° C., 30° C., 35° C., 40°C., 45° C., 50° C., 55° C., 60° C., 65° C., 70° C., 75° C., 80° C., 85°C., 90° C., 95° C. or 100° C. cooler than the liquid phase.

By specifically controlling the head space temperature and pressure, theinventors of the present invention found that this results in animprovement in the rate of conversion of nitrogen oxides to nitric acidin the vapor space. Specifically, the inventors found that cooling theheadspace below the temperature of the liquid phase improved (namely,increased) the overall rate of nitric acid regeneration (as evidence bya reduction in the number of units of nitrogen oxides (such as NO₂)generated in the headspace. Increasing the rate of nitric acidregeneration allows the oxidation process in this invention to use lessnitric acid than previously described to achieve the same degree ofoxidation. In addition, the process of the present invention is moreeconomical because less nitric acid is lost during pressure controlventing of the reaction and during the recovery steps of the processdiscussed later herein. In other words, the method of the presentinvention results in a “low waste” oxidation process which has notexisted previously. As used herein, the term “low waste” means that lessthan 1%, less than 0.9%, less than 0.8%, less than 0.7%, less than 0.6%,less than 0.5%, less than 0.4%, less than 0.3%, less than 0.2%, lessthan 0.1% of nitric acid is lost during the process of the presentinvention during pressure control venting of the reaction and during therecovery steps. Additionally, controlling the headspace temperature asdescribed herein results in the reaction vessel having to be vented lessfrequently or not at all during the oxidation process, specifically whencompared with process that does not control the headspace temperature asdescribed herein.

The process of the present invention requires exposing the firstreaction mixture to the positive pressure of oxygen. Therefore, oxygenis added at point at time and at some location in the one or morereaction vessels. The addition of oxygen and the location of itsaddition may be during the formation of the initial or first reactionmixture. Alternatively, in another aspect, oxygen can be added in thelast reactor or only reactor (if only a single reactor comprises thereaction train). Still further alternatively, oxygen may be added at aselected reactor in the reaction vessel train. Still furtheralternatively, oxygen can be to each individual reaction vesselcomprising the reaction vessel train. The oxygen may be introduced intothe first reaction mixture by any means known in the art, includingbubbling gaseous oxygen through the reaction mixture. The oxygen addedto the reaction vessel train can be added cocurrently orcountercurrently or both cocurrently and countercurrently. The pressurewithin the reaction vessel generally ranges from above about 0 barg toabout 1000 barg. In one aspect, the pressure can range from about 1 bargto about 1000 barg, about 5 barg to about 1000 barg, about 10 barg toabout 1000 barg, 20 barg to about 1000 barg, about 30 barg to about 1000barg, about 40 barg to about 1000 barg, 50 barg to about 1000 barg,about 60 barg to about 1000 barg, about 70 barg to about 1000 barg,about 80 barg to about 1000 barg, about 90 barg to about 1000 barg,about 100 barg to about 1000 barg, about 200 barg to about 1000 barg,about 300 barg to about 1000 barg, about 400 barg to about 1000 barg,about 50 barg to about 1000 barg, 0 barg to about 900 barg, 1 barg toabout 900 barg, about 5 barg to about 900 barg, about 10 barg to about900 barg, 20 barg to about 900 barg, about 30 barg to about 900 barg,about 40 barg to about 900 barg, 50 barg to about 900 barg, about 60barg to about 900 barg, about 70 barg to about 900 barg, about 80 bargto about 900 barg, about 90 barg to about 900 barg, about 100 barg toabout 900 barg, about 200 barg to about 900 barg, about 300 barg toabout 900 barg, about 400 barg to about 900 barg, about 50 barg to about900 barg, 0 barg to about 800 barg, 1 barg to about 800 barg, about 5barg to about 800 barg, about 10 barg to about 800 barg, 20 barg toabout 800 barg, about 30 barg to about 800 barg, about 40 barg to about800 barg, 50 barg to about 800 barg, about 60 barg to about 800 barg,about 70 barg to about 800 barg, about 80 barg to about 800 barg, about90 barg to about 800 barg, about 100 barg to about 800 barg, about 200barg to about 800 barg, about 300 barg to about 800 barg, about 400 bargto about 800 barg, about 50 barg to about 800 barg, 0 barg to about 700barg, 1 barg to about 700 barg, about 5 barg to about 700 barg, about 10barg to about 700 barg, 20 barg to about 700 barg, about 30 barg toabout 700 barg, about 40 barg to about 700 barg, 50 barg to about 700barg, about 60 barg to about 700 barg, about 70 barg to about 700 barg,about 80 barg to about 700 barg, about 90 barg to about 700 barg, about100 barg to about 700 barg, about 200 barg to about 700 barg, about 300barg to about 700 barg, about 400 barg to about 700 barg, about 50 bargto about 700 barg, 0 barg to about 600 barg, 1 barg to about 600 barg,about 5 barg to about 600 barg, about 10 barg to about 600 barg, 20 bargto about 600 barg, about 30 barg to about 600 barg, about 40 barg toabout 600 barg, 50 barg to about 600 barg, about 60 barg to about 600barg, about 70 barg to about 600 barg, about 80 barg to about 600 barg,about 90 barg to about 600 barg, about 100 barg to about 600 barg, about200 barg to about 600 barg, about 300 barg to about 600 barg, about 400barg to about 600 barg or about 50 barg to about 600 barg. In stillanother aspect, the pressure can range from about 1 barg to about 200barg, about 5 barg to about 200 barg, about 10 barg to about 200 barg,about 20 barg to about 200 barg, about 30 barg to about 200 barg, about40 barg to about 200 barg, about 50 barg to about 200 barg, 1 barg toabout 100 barg, about 5 barg to about 100 barg, about 10 barg to about100 barg, about 20 barg to about 100 barg, about 30 barg to about 100barg, about 40 barg to about 100 barg, about 50 barg to about 100 barg,1 barg to about 50 barg, about 5 barg to about 50 barg, about 10 barg toabout 50 barg, about 20 barg to about 50 barg, about 30 barg to about 50barg, or about 40 barg to about 50 barg.

The first reaction mixture flows through the one or more reactionvessels or reaction vessel train under the controlled temperature andcontrolled positive pressure of oxygen as described previously herein(namely, a controlled temperature of from about 5° C. to about 105° C.and a controlled positive pressure of oxygen from about 0 barg to about1000 barg) for a period of time suitable to oxidize the organiccompounds in the first reaction mixture to form a subsequent (or second)reaction mixture that comprises a mixture of organic acid products andnitrogen oxides (namely, N₂O₃, N₂O₄, NO, NO₂ and N₂O).

Once this subsequent (final) reaction mixture is formed, it is contactedwith, delivered or recirculated to the vapor or headspace of one or morereaction vessels. If multiple reaction vessels are used, the subsequent(final) reaction mixture can be contacted, delivered or recirculated inany of the reaction vessels that contain the subsequent (final) reactionmixture. For example, recirculation may occur in the last or second tolast reaction vessel comprising the reaction train.

The step of contacting, delivering or recirculating is important in theprocess of the present invention. Specifically, the contacting, deliveryor recirculation step is used convert or recycle the nitrogen oxidescontained in the subsequent (final) reaction mixture and gases back tonitric acid (HNO₃). This “converted” or “recycled” nitric acid can bereused in the oxidation process through methods described herein.

The contacting, delivering or recirculating can be conducted using anytechnique known in the art provided that a means is used that providesfor a high surface area of contact between the gas and liquid phasescontained in the subsequent final reaction mixture thereby allowing thenitrogen oxides to be converted or recycled back to nitric acid. Themost important aspect is that some means is used to increase the surfacearea. Basically, any means for creating a high surface area of contactbetween the gas and liquid phases contained in a reaction vessel can beused in the process of the present invention. For example, the reactionvessel can comprise a pump at the bottom and a spray nozzle at the top.The pump transports the subsequent (final) reaction mixture to the topof the reaction vessel to one or more spray nozzles which spray thereaction mixture into the reaction vessel thereby creating a highsurface area of contact. Alternatively, a falling film contactor orpacked bed (such as a random, structured, or anything that can causehigh surface area contact as known by those skilled in the art), whereliquid is pumped from the bottom to the top of a device that createshigh surface area as the liquid drops through the tubes of a heatexchanger or a high surface area bed can be used. Alternatively, a highsurface area of contact between the gas and liquid phases contained inthe subsequent (final) reaction mixture can be created by employing anagitator which can be used to create a high rate of agitation (eitherhorizontal or vertical) in one or more reaction vessels therebyresulting in the reaction mixture being thrown or pushed into the vaporspace above the liquid. High rates of agitation using an agitator in oneor more reaction vessels employed in the process of the presentinvention can be determined using routine techniques known to thoseskilled in the art.

While conducting an experiment to understand if improving the masstransfer between the gas and liquid phases the reaction would speed upthe reaction, the inventors surprisingly discovered that the oxidationreaction rates did not increase and in fact, the oxidation was quenchedand conversion of the organic substrate into organic acid products wasstopped. Specifically, the inventors found that when the subsequent(final) reaction mixture was sprayed from one or more spray nozzles atthe top of the reaction vessel during this contacting, delivering orrecirculating step, that the oxidation reaction immediately terminated,which was immediately identified/recognized by reduced cooling load andthe colors of the NOX gas and liquids changing from dark to clearrelatively quickly. This surprising result may be used to control theenergetic oxidation reaction, particularly in preventing over oxidationof the organic substrate once the desired level of oxidation has beenreached. This is particularly effective when combined with improvednitric acid regeneration (discussed more in the next paragraph below)through cooling of the headspace which leads to faster oxidation ratesand makes control over the degree of oxidation difficult to control.

Additionally, the inventors also discovered that the contacting,delivering or recirculating step allowed for the more efficient recoveryof nitric acid as the nitric compounds were more quickly converted tonitric acid due to the efficient contact of the vapor and liquid. Theinventors believe that the reason the reaction is terminated with thisstep is that the nitrogen oxides contained in both the headspace and thesubsequent (final) reaction mixture are converted back to nitric acid.Once the contacting, delivering or recirculating (recirculation) step iscompleted and the nitrogen oxides converted to nitric acid, then thenitric acid can be recovered or removed from the subsequent (final)reaction mixture to give a final reaction mixture of organic acids thatare suitable for further processing. The nitric acid can be recovered orremoved from the subsequent reaction mixture using any technique knownin the art. For example, evaporation, distillation, nanofiltration,diffusion dialysis or alcohol or ether precipation can be used.Regardless of the technique used, a significant portion of the nitricacid is removed from the subsequent (final) reaction mixture. In oneaspect, the term “significant” when used in connection with removal ofnitric acid from the subsequent (final) reaction mixture means that atleast 65% of the nitric acid is removed from the subsequent (final)reaction mixture. In another aspect, the term “significant” when used inconnection with removal of nitric acid from the subsequent (final)reaction mixture means that at least 70% of the nitric acid is removedfrom the subsequent (final) reaction mixture. In still yet anotheraspect, the term “significant” when used in connection with removal ofnitric acid from the subsequent (final) reaction mixture means that atleast 75% of the nitric acid is removed from the subsequent (final)reaction mixture. In still yet another aspect, the term “significant”when used in connection with removal of nitric acid from the subsequent(final) reaction mixture means that at least 80% of the nitric acid isremoved from the subsequent (final) reaction mixture. In another aspect,the term “significant” when used in connection with removal of nitricacid from the subsequent (final) reaction mixture means that at least85% of the nitric acid is removed from the subsequent (final) reactionmixture. In another aspect, the term “significant” when used inconnection with removal of nitric acid from the subsequent (final)reaction mixture means that at least 90% of the nitric acid is removedfrom the subsequent (final) reaction mixture. In another aspect, theterm “significant” when used in connection with removal of nitric acidfrom the subsequent (final) reaction mixture means that at least 95% ofthe nitric acid is removed from the subsequent (final) reaction mixture.In another aspect, the term “significant” when used in connection withremoval of nitric acid from the subsequent (final) reaction mixturemeans that at least 99% of the nitric acid is removed from thesubsequent (final) reaction mixture. In another aspect, the term“significant” when used in connection with removal of nitric acid fromthe subsequent (final) reaction mixture means that 99.9% of the nitricacid is removed from the subsequent (final) reaction mixture. Forexample if the nitric acid is to be removed by evaporation, anyevaporator known in the art can be used. Examples of evaporators thatcan be used in the process of the present invention include, but are notlimited to, vertical-pipe, horizontal-pipe, slanting-pipe, rotor orthin-layer, centrifugal, worm and falling-film evaporators, tube-bundleevaporators, basket evaporators, high viscosity evaporators, evaporatorswith one or more scrubbers, evaporators with one or more boilers,evaporators with one or more distillation columns, evaporators withexternal return pipe and forced circulation, evaporators with externalheating elements and forced circulation and other evaporators known tothose skilled in the art. In one aspect, the method of evaporationcomprises the use of at least one wiped film evaporator. In analternative aspect, the method of evaporation comprises the use of atleast two wiped film evaporators. In yet another aspect, the method ofevaporation comprises the use of a wiped film evaporator and anothertype of evaporator such as a vertical-pipe evaporator, a horizontal-pipeevaporator, a basket evaporator, etc. In one aspect, more than oneevaporator is used in the reaction train. In one aspect, more than twoevaporators are used in the reaction train. In another aspect, more thanthree evaporators are used in the reaction train. In yet another aspect,more than four evaporators are used in the reaction train. In stillanother aspect, more than one evaporator is used in the reaction trainin which at least one evaporator contains a scrubber, condenser or adistillation column. In still another aspect, more than two evaporatorsare used in the reaction train in which at least one evaporator containsa scrubber, condenser or a distillation column. In still another aspect,more than three evaporators are used in the reaction train in which atleast one evaporator contains a scrubber, condenser or a distillationcolumn. In still another aspect, more than four evaporators are used inthe reaction train in which at least one evaporator contains a scrubber,condenser or a distillation column.

Alternatively, as mentioned previously, the nitric acid can be removedfrom the subsequent (final) reaction mixture using diffusion dialysis.Diffusion dialysis can be used to remove nitric acid from the reactionmixture instead of or in conjunction with an evaporator. This process istypically used for the separation of common inorganic acids such ashydrochloric acid, sulfuric acid, or nitric acid from multivalent metalcations such as Cu²⁺ or Zn²⁺. The aqueous acid feedstock of theinorganic acid and metal salt(s) and a separate water stream are routedthrough a diffusion dialysis system consisting of low pressure pumps andan appropriate membrane system. Two aqueous exit streams are generated,an acid recovery stream comprised primarily of inorganic acid with somemetal salt(s), and a product recovery stream comprised of primarilymetal salt(s) with some inorganic acid. The separate streams can besubjected to further diffusion dialysis as needed to give a stream withhigher inorganic acid concentration and lower metal salt concentrations,and a stream with higher metal salt concentration and lower inorganicacid concentration. This separation technique was applied to nitric acidoxidation reaction mixtures as prepared by the described methods herein,and was found to perform in the same manner as used in separation ofinorganic acids from metal salts. The bulk of the nitric acid with someorganic acid products, was in the acid recovery stream, and the bulk ofthe organic acid products with some of the nitric acid, was in theorganic product recovery stream. The use of this technology to separatenitric acid from the organic acid products produced from the oxidationprocess described here is a very low energy process, operates at ambienttemperature, and can be run continuously. It offers an additionaladvantage over direct evaporation/distillation of nitric acid from thereaction mixture in that in the latter process, additional oxidativeprocesses can occur generating additional nitrogen oxide gases that haveto be contained, removed and/or converted to oxides of nitrogen that areconvertible to nitric acid. In contrast, the diffusion dialysis processoperates at dilute concentrations and the recovered nitric acid streamfrom the diffusion dialysis process is low in carbohydrate productcontent and evaporation/distillation of the recovered nitric acid isachieved with minimal oxidation and nitrogen oxide formation occurringduring nitric acid recovery.

It is recognized that the final reaction mixture from which nitric acidhas been removed may be made basic to convert any residual or remainingnitric acid to inorganic nitrate, and converting the organic acids to amixture of organic acid salts. Neutralization to a pH greater than 7with inorganic base, without removal of nitric acid, requires base forall of the nitric acid plus the organic acids and the nitric acid is notdirectly recovered for further use. In contrast, partial recovery of thenitric acid for reuse by vacuum distillation is advantageous because therecovered nitric acid can be used again for oxidation purposes, althoughit is difficult to remove all the residual nitric acid from the syrupyconcentrate with ease.

Depending upon the starting organic compounds, the specific reactionconditions employed, and the target products, this solution can betreated accordingly to give the organic acids in one or more forms.Organic acids can be obtained in free acid forms, as disalts, monosalts, acid lactones, and/or dilactones, or as mixtures of various saltforms, and/or acid and/or acid lactone forms. Acids generated fromoligosaccharides and other higher molecular weight carbohydrates aremixtures which can contain some of the above aldonic and aldaric acidsplus higher molecular weight acids derived from higher molecular weightcarbohydrates. These acids can be also be obtained in various acid,lactone and salt forms.

Additionally, when oxidation products are obtained from directconcentration of the reaction mixture that removes most of the nitricacid, or by subjecting the oxidation reaction mixture to diffusiondialysis followed by removal of the bulk of the remaining nitric acid byan evaporation/distillation step, residual nitric acid can be removed asnitrate and recovered by a membrane filtration method. When theresultant syrupy product/residual nitric acid mixture is treated with aninorganic base to a pH greater than 7, the resulting solution containsinorganic nitrate and the salt(s) of the product organic acids. Thissolution is then subjected to filtration, typically nanofiltration, withthe bulk of inorganic nitrate passing through the membrane and into thepermeate, and the bulk of the organic product remaining in theretentate. The prior art has reported removal of inorganic nitrate fromorganic acid salts after nitric acid oxidation using ion retardationchromatography (See, D. E. Kiely and G. Ponder, U.S. Pat. No. 6,049,004,Apr. 11, 2000). However, ion retardation chromatography is not as fast,not as applicable on a large scale, and not as efficient as thefiltration methods described herein. In the oxidation processes of thecurrent invention, the remaining retentate contains the organic acidsalt forms with minimal inorganic salt content. The presence of onlysmall amounts of inorganic nitrate in the organic acid salt productsrenders purification and/or isolation of the organic acid salt productsor non-salt products greatly improved over previously reported methods.

In an alternative aspect, the current invention also comprises a mixtureof one or more organic acids, produced by the oxidation methodsdescribed herein. The mixture of one or more organic acids may be theresult of the oxidation of a variety of organic compounds. The mixtureof one or more organic acids generally includes the oxidation productsof monohydric alcohols, diols, polyols, aldehydes, ketones,carbohydrates, and mixtures thereof. Non-limiting examples ofcarbohydrates suitable for oxidation by the processes of the currentinvention include, but are not limited to, monosaccharides, such as thecommon monosaccharides D-glucose, D-mannose, D-xylose, L-arabinose,D-arabinose, D-galactose, D-arabinose, D-ribose, D-fructose;disaccharides, such as the common disaccharides maltose, sucrose,isomaltose, and lactose; oligosaccharides, for example, maltotriose andmaltotetrose; aldonic acids such as D-gluconic acid, D-ribonic acid, andD-galactonic acid; glucoheptonic acid; aldonic acid esters, lactones andsalts that include but are not limited to those derived from D-gluconicacid, D-ribonic acid, glucoheptonic acid, and D-galactonic acid;alduronic acids, for example, D-glucuronic acid and L-iduronic acid;alduronic esters, lactones and salts that include but are not limited tothose derived from D-glucuronic acid and L-iduronic acid; alditols thatinclude glycerol, threitol, erythritol, xylitol, D-glucitol; alditolswith more than six carbon atoms; cyclitols, for example common cyclitolssuch as myo-inositol and scyllitol; corn syrups with different dextroseequivalent values; other aldonic acids and salts thereof, such as,glucoheptonic acids, glycerbionic acids, erythrobionic acids,threobionic acids, ribobionic acids, arabinobionic acids, xylobionicacids, lyxobionic acids, allobionic acids, altrobionic acids,glucobionic acids, mannobionic acids, gulobionic acids, idobionic acids,galactobionic acids, talobionic acids, alloheptobionic acids,altroheptobionic acids, glucoheptobionic acids, mannoheptobionic acids,guloheptobionic acids, idoheptobionic acids, galactoheptobionic acidsand taloheptobionic acids; glycols such as ethylene glycol, diethyleneglycols, triethylene glycols or mixtures thereof; mixtures ofcarbohydrates from different biomass, plant or microorganism sources;polysaccharides from biomass, plant or microorganism sources (such asstarch or celluloses) and of varying structures, saccharide units andmolecular weights.

Additionally, the mixture of one or more organic acids may include theacid or salt forms of the oxidized organic compound. Suitable examplesof organic acid salts include, but are not limited to sodium hydrogenglucarate, potassium hydrogen glucarate, lithium hydrogen glucarate,disodium glucarate, sodium potassium glucarate, dipotassium glucarate,dilithium glucarate, lithium sodium glucarate, lithium potassiumglucarate, zinc glucarate, calcium glucarate, sodium hydrogen xylarate,potassium hydrogen xylarate, lithium hydrogen xylarate, disodiumxylarate, sodium potassium xylarate, dipotassium xylarate, dilithiumxylarate, lithium sodium xylarate, lithium potassium xylarate, zincxylarate, calcium xylarate, sodium gluconate, potassium gluconate,lithium gluconate, disodium gluconate, sodium potassium gluconate,dipotassium gluconate, dilithium gluconate, lithium sodium gluconate,lithium potassium gluconate, zinc gluconate, calcium gluconate, sodiumgalactarate, potassium galactarate, lithium galactarate, disodiumgalactarate, sodium potassium galactarate, dipotassium galactarate,dilithium galactarate, lithium sodium galactarate, lithium potassiumgalactarate, zinc galactarate, calcium galactarate, sodium hydrogentartarate, potassium tartarate, lithium hydrogen tartarate, disodiumtartarate, sodium potassium tartarate, dipotassium tartarate, dilithiumtartarate, lithium sodium tartarate, lithium potassium tartarate, zinctartarate, sodium hydrogen tartronate, potassium hydrogen tartronate,lithium hydrogen tartronate, disodium tartronate, sodium potassiumtartronate, dipotassium tartronate, dilithium tartronate, lithium sodiumtartronate, lithium potassium tartronate, zinc tartronate, calciumtartronate, sodium hydrogen oxalate, potassium hydrogen oxalate, lithiumhydrogen oxalate, disodium oxalate, sodium potassium oxalate,dipotassium oxalate, dilithium oxalate, lithium sodium oxalate, lithiumpotassium oxalate, zinc oxalate, calcium oxalate, sodium glycolate,potassium glycolate, lithium glycolate, disodium glycolate, sodiumpotassium glycolate, dipotassium glycolate, dilithium glycolate, lithiumsodium glycolate, lithium potassium glycolate, zinc glycolate, calciumglycolate, sodium glycerate, potassium glycerate, lithium glycerate,zinc glycerate, calcium glycerate, and combinations thereof. In anotheraspect, the hydroxycarboxylic acid may include, but is not limited to,disodium glucarate, sodium potassium glucarate, dipotassium glucarate,zinc glucarate, disodium xylarate, sodium potassium xylarate,dipotassium xylarate, zinc xylarate, disodium galactarate, sodiumpotassium galactarate, dipotassium galactarate, zinc galactarate, andcombinations thereof.

EXAMPLES Example 1 General Methods for High Surface Area Contact forExamples 2-3

Oxidations were carried out in a Metler Toledo Labmax reactor which isdesigned to operate under computer control. The Labmax was fitted withan overhead agitation motor that drove a stir shaft fitted with ananchor style agitation paddle. The reactor was made of glass and had asilicon oil filled jacket for cooling and heating. In addition, theLabmax was fitted with an overhead balance in communication with ametering pump for controlled dosing of reactants into the reactor, andresistance temperature detector (“RTD”) temperature probes to measurethe temperature of both the reactor contents and the reactor jacket oil.A Mettler Toledo LMPress 60 pressure controller was used to maintainoxygen pressure of 1.0 barg+/−0.04 barg within the reactor. A pressuremanifold fitted with a pressure relief valve, a rupture disc, and apressure gauge was added to the head of the reactor. The Labmax wascontrolled using iControlLabmax software version 4.0 which allows theuser to specify reaction parameters, measures and logs data, and usesproportional integral derivative (PID) loop processing to maintainstable material temperatures during a reaction and dose reactants intothe reactor at a given rate.

Example 2 Oxidation Quenching by Circulation, Comparison ofNon-Circulated and Circulated Oxidations

411 g (4.5 moles) of concentrated nitric acid was added to the reactorand the iControl software was used to maintain a reaction temperature of25° C. and an agitation speed of 200 RPM for the duration of thereaction. Immediately after the nitric acid was added 0.31 g (4.5millimoles) of sodium nitrite was added to the reactor and the reactorwas sealed and pressurized with 1 barg oxygen. 62.5% D-glucose solutionwas dosed into the reactor at a rate of 2.88 g/min until 432.4 g (1.5moles) had been added (150 min) After a short induction period, themixture began to react exothermically as indicated by the jackettemperature having to run at colder and colder temperatures to maintainthe material temperature of 25° C. After 35 minutes, the jackettemperature was running at 4.5° C. to maintain a reaction temperature of25° C. The headspace filled with dark brown NO₂ gas and the liquidmixture turned dark green. At this time, the reaction began to slowlysubside taking about 6 hours for the jacket temperature to rise to 20°C. to maintain a reaction temperature of 25° C. The headspace continuedto be filled with dark brown gasses and the liquid mixture continued tobe dark green in color until the reaction was fully quenched/terminatedby adding a liter of cold water to the reactor. The exothermicity, gasproduction, and green liquid color observations were shown to be typicalof all nitric acid oxidations performed in a closed vessel under oxygenpressure regardless of molar ratio or batch size.

Next, an identical reaction was performed except this time atapproximately 25 minutes into the oxidation, a recirculation pump wasturned on and the material was sprayed into the headspace of the reactorat a rate of about 75 ml/min so that the material was removed from thebottom of the reactor and sprayed through the headspace of the reactorand back onto the liquid surface for the duration of the reactionImmediately, the reaction began consuming oxygen indicated by the LMPress 60 having to increase its oxygen flow rate to the reactor in orderto maintain the 1 barg pressure, and the brown NO₂ gas in the headspacebegan to dissipate resulting in a colorless headspace and the emeraldgreen color in the liquid lightened up. The increased consumption ofoxygen is an indication that NO_(x) species are being oxidized back tonitric acid because the oxidation not only consumes oxygen but alsoresults in a net pressure loss which must be made up with more oxygen.Within a few minutes, the exothermicity of the oxidation wassignificantly reduced indicated by the jacket temperature running at 17°C. to maintain the same operating temperature (a 63% reduction in deltaT between jacket and material temperatures when compared to thenon-circulated batch at the same time point). The reduction inexothermicity was an indication that the oxidation rate was slowing downand the reaction was being quenched. The green color in the liquid beganto fade to pale yellow over the course of 1 hour. The early consumptionof oxygen, and the reduction in exothermicity, gas production, and greenliquid color were all indications of the oxidation being quenched orslowed down by the recirculation.

Example 3 Circulated Oxidation

205.5 g (2.25 moles) of 69% nitric acid was added to the reactor and theiControl software was used to maintain a reaction temperature of 25° C.and an agitation speed of 200 RPM for the duration of the reaction. 0.46g (6.7 millimoles) of sodium nitrite was added to the reactor and thereactor was sealed and pressurized with 1 barg oxygen. Then 62.5%D-glucose solution was dosed into the reactor at a rate of 2.88 g/minuntil 648.6 g (2.25 moles) had been added (225 min) After about 20minutes, the mixture began to react exothermically and brown NO_(x)gases began to fill the headspace of the reactor and the liquid contentsof the reactor turned emerald green in color. At this time, arecirculation pump was turned on and the material was sprayed into theheadspace of the reactor at a rate of about 75 ml/min so that thematerial was removed from the bottom of the reactor and sprayed throughthe headspace of the reactor and back onto the liquid surface for theduration of the reaction. Immediately, the reaction began consumingoxygen indicated by the LM Press 60 having to increase its oxygen flowrate to the reactor in order to maintain the 1 barg pressure, and thebrown NO₂ gas in the headspace began to dissipate resulting in acolorless headspace. The increased consumption of oxygen is anindication that NO_(x) species are being oxidized back to nitric acidbecause the oxidation not only consumes oxygen but also results in a netpressure loss which must be made up with more oxygen. Within a fewminutes, The exothermicity of the oxidation was significantly reducedindicated by a 13° C. increase in jacket temperature to maintain thesame operating temperature (an 86% reduction in delta T between thejacket temperature and the material temperature). The reduction inexothermicity was an indication that the oxidation rate was slowing downand the reaction was being quenched. The green color in the liquid beganto fade to pale yellow over the course of 1 hour. The early consumptionof oxygen, and the reduction in exothermicity, gas production, andreduction in green liquid color were all indications of the oxidationbeing quenched or slowed down by the recirculation.

Example 4 General Methods for Examples 5-6

Oxidations were carried out in a Metler Toledo Labmax reactor which isdesigned to operate under computer control. The Labmax was fitted withan overhead agitation motor that drove a stir shaft fitted with fourpropeller type agitation paddles spaced equally throughout the height ofthe reactor. The reactor was made of glass and had a siliconoil filledjacket for cooling and heating. In addition, the Labmax was fitted withan overhead balance in communication with a metering pump for controlleddosing of reactants into the reactor, and RTD temperature probes tomeasure the temperature of both the reactor contents and the reactorjacket oil and a type K thermocouple was used to measure the temperatureof the headspace. A Mettler Toledo LMPress 60 with a pressure transducerand internal PID loop processing was used to maintain oxygen pressure of1.0 barg+/−0.04 barg within the reactor. A pressure manifold fitted witha pressure relief valve, a rupture disc and a pressure gauge was addedto the head of the reactor. The reactor was equipped with a stainlesssteel condenser coil that extended inside the reactor from the top toabout half way down the reactor. This condenser coil could be used tocool the top portion of the reactor independently of the oil jacket. TheLabmax was controlled using iControl Labmax software version 4.0 whichallows the user to specify reaction parameters, measures and logs data,and uses PID loop processing to maintain stable material temperaturesduring a reaction and dose reactants into the reactor at a given rate.The headspace of the reactor was plumbed into an external FT-IR gas cellwith valves allowing gas samples to be removed from the headspace of thereactor. The gas cell was fitted into a Thermo Scientific AntarisIndustrial Gas System (IGS) which could be used to take FT-IR spectra ofthe gas samples in real time. All spectra were obtained using theaverage of 8 scans from 700-3900 wavenumbers (i.e., inverse centimeters)and a resolution of 0.5 wavenumbers. The IGS was calibrated usingcertified gas standards. The gas standards were diluted with nitrogenusing an Environics 4040 Diluter which allows the user to flow standardgas and nitrogen through the cell at predetermined flow rates in orderto achieve desired gas concentrations. A 10-point calibration curve wasgenerated for each gas analyzed. Due to the equilibrium relationship ofNO₂ and its dimer N₂O₄, the concentrations of both species are expressedin terms of total NO₂ units where total NO₂ units equals theconcentration of NO₂ plus two times the concentration of N₂O₄.

Example 5 Oxidation of NO₂ to Nitric Acid by Headspace Cooling,Comparison of Headspace Cooling and no Headspace Cooling

1238.9 g (13.5 moles) of concentrated nitric acid was added to thereactor and the iControl software was used to maintain a reactiontemperature of 25° C. for 3 hours and 25 minutes then increase to 30° C.for 45 min then increase again to 35° C. for 75 min. An agitation speedof 100 RPM was used for the duration of the reaction. 0.93 g (13.5millimoles) of sodium nitrite was added to the reactor and the reactorwas sealed and pressurized with 1 barg oxygen. 62.5% D-glucose solutionwas dosed into the reactor at a variable rate starting at 3.12 g/min andgradually increasing to 14.9 g/min until 1297.2 g (7.20 moles) had beenadded (205 min) After about 20 minutes, the mixture began to reactexothermically as indicated by the jacket temperature needing to run atcolder and colder temperatures to maintain the material temperature of25° C. Gas samples were taken from the reactor every 20 minutes andanalyzed with FT-IR for composition and quantification. After 25minutes, brown NO_(x) gasses began to fill the headspace of the reactorand the liquid contents of the reactor turned emerald green in color.After 4.5 hours, the total NO₂ units concentration had built to 70% inthe headspace of the reactor then slowly decreased to about 59% at theend of the oxidation. Despite the liquid temperature being maintained at25° C.-35° C., the temperature of the headspace slowly built to amaximum of 40° C. reaching this maximum at the same time the total NO₂units concentration reached a max of 70%. This temperature build was dueto the exothermic reaction 2 NO+O₂≈2 NO₂.

Then an identical oxidation was performed except this time the headspacecondenser was activated and allowed to run at −12° C. for the durationof the experiment. After 25 minutes, brown NO_(x) gasses began to fillthe headspace of the reactor and the liquid contents of the reactorturned emerald green in color. After 4.5 hours the total NO₂ unitsconcentration had built to 55% in the headspace of the reactor thenslowly decreased to about 50% at the end of the oxidation. The headspacecondenser was able to keep the temperature of the headspace below 20° C.despite the exothermic reaction 2 NO+O₂≈2 NO₂. This lower temperatureshifts the equilibrium of the dimerization of NO₂ to N₂O₄ allowing formore N₂O₄ to form which then enables N₂O₄ to condense into the liquidphase. Once in the liquid phase the N₂O₄ reacts with water to make HNO₃and HNO₂ according to the reaction N₂O₄+H₂O≈HNO₂+HNO₃. The higherconcentration of nitric acid in the liquid phase was indicated by thelower concentration of total NO₂ units in the gas phase. At the end ofthe oxidation, the jacket temperature of the reactor was adjusted sothat the headspace could be cooled to 5° C. This resulted in the totalNO₂ units concentration in the headspace gradually diminishing to 18%over a 60 min period allowing for more nitric acid recovery (a 74%reduction in NO₂ concentration compared to the non headspace cooledexperiment).

Example 6 Oxidation of NO₂ to Nitric Acid by Headspace Cooling,Comparison of Headspace Cooling and no Headspace Cooling

1110 g (12.2 moles) of concentrated nitric acid was added to thereactor. Then 1.1 g (15.9 millimoles) of sodium nitrite and 1753 g ofthe above dextrose solution (6.1 moles) were added to the reactor andthe iControl software was used to maintain a reaction temperature of 35°C. and an agitation speed of 300 RPM was used for the duration of thereaction. The reactor was then sealed and pressurized with 1 bargoxygen. After a short induction period, the mixture began to reactexothermically as indicated by the jacket temperature needing to run atcolder and colder temperatures to maintain the material temperature of25° C. Gas samples were taken from the reactor periodically and analyzedwith FT-IR for composition and quantification. After about 30 minutes,brown NO_(x) gasses began to fill the headspace of the reactor and theliquid contents of the reactor turned emerald green in color. After 3.9hours the total NO₂ units concentration had built to 57% in theheadspace of the reactor then slowly decreased to about 46% at the endof the oxidation.

Then an identical oxidation was performed except in this experiment theheadspace condenser was activated and allowed to run at −12° C. for theduration of the experiment. After about 30 minutes, brown NO_(x) gassesbegan to fill the headspace of the reactor and the liquid contents ofthe reactor turned emerald green in color. After 3.9 hours the total NO₂units concentration had built to 50.0% in the headspace of the reactorthen slowly decreased to about 40% at the end of the oxidation. Theheadspace condenser was able to keep the temperature of the headspacebelow 20° C. despite the exothermic reaction 2 NO+O₂≈2 NO₂. This lowertemperature shifts the equilibrium of the dimerization of NO₂ to N₂O₄allowing for more N₂O₄ to form then enables N₂O₄ to condense into theliquid phase. Once in the liquid phase the N₂O₄ can react with water tomake HNO₃ and HNO₂ according to the reaction N₂O₄+H₂O≈HNO₂+HNO₃. Thehigher concentration of nitric acid in the liquid phase was indicated bythe lower concentration of total NO₂ units in the gas phase. At the endof the oxidation, the jacket temperature of the reactor was adjusted sothat the headspace could be cooled to −8° C. This resulted in the totalNO₂ units concentration in the headspace gradually diminishing to 13%over a 60 min period allowing for more nitric acid recovery (a 77%decrease in total NO₂ units concentration compared to the no headspacecooling experiment).

Example 7 General Methods for Examples 8-11

Oxidations were carried out in a Metler Toledo Labmax reactor which isdesigned to operate under computer control. The Labmax was fitted withan overhead agitation motor that drove a stir shaft fitted withagitation paddles. Both glass and stainless steel reactors were used thereactors were equipped with silicon oil filled jackets for cooling andheating. In addition, the Labmax was fitted with an overhead balance incommunication with a metering pump for controlled dosing of reactantsinto the reactor, and RTD temperature probes to measure the temperatureof both the reactor contents and the reactor jacket oil and a type Kthermocouple was used to measure the temperature of the headspace. AMettler Toledo LMPress 60 with a pressure transducer and internal PIDloop processing was used to maintain oxygen pressure within the reactor.A pressure manifold fitted with a pressure relief valve, a rupture discand a pressure gauge was added to the head of the reactor. The Labmaxwas controlled using iControl Labmax software version 4.0 which allowsthe user to specify reaction parameters, measures and logs data, anduses PID loop processing to maintain stable material temperatures duringa reaction and dose reactants into the reactor at a given rate. Theheadspace of the reactor was plumbed into an external FT-IR gas cellwith valves allowing gas samples to be removed from the headspace of thereactor. The gas cell was fitted into a Thermo Scientific AntarisIndustrial Gas System (IGS) which could be used to take FT-IR spectra ofthe gas samples in real time. All spectra were obtained using theaverage of 8 scans from 700-3900 wavenumbers (i.e., inverse centimeters)and a resolution of 0.5 wavenumbers. The IGS was calibrated usingcertified gas standards. The gas standards were diluted with nitrogenusing an Environics 4040 Diluter which allows the user to flow standardgas and nitrogen through the cell at predetermined flow rates in orderto achieve desired gas concentrations. A 10-point calibration curve wasgenerated for each gas analyzed. Due to the equilibrium relationship ofNO₂ and its dimer N₂O₄, the concentrations of both species are expressedin terms of total NO₂ units where total NO₂ units equals theconcentration of NO₂ plus two times the concentration of N₂O₄.

Example 8 NO_(x) Oxidation by Headspace Cooling. Comparison of HeadspaceCooling vs. no Headspace Cooling

Two side-by-side oxidations were performed for which all parameters werekept identical except for the use of headspace cooling. In bothoxidations, 1.70 grams sodium nitrite was dissolved in 2,716 grams of62.5% D-glucose solution then the mixture was loaded into a 7 literstainless steel reactor. The reactor had separate cooling jackets andseparate internal cooling coils for the top and bottom halves allowingfor separate temperatures to be maintained in the gas and liquid phasesof the reactor. The gas and liquid phases were agitated using anoverhead stirring motor attached to an agitation shaft with one turbineimpeller in the liquid phase and three impellers in the gas phase. Thelower cooling system was used to maintain the glucose mixture at 20° C.1,720 grams of 69% nitric acid was added to the mixture, the reactor waspurged to reach a minimal amount of atmospheric gases and thenpressurized with 4 barg of oxygen. For the headspace cooling experiment,the upper cooling system was adjusted to provide a surface temperatureof −12° C. in the gas phase of the reactor and for the non-headspacecooled experiment no temperature control was used for the top half ofthe reactor. The mixture was allowed to react for 5.5 hours continuallyadjusting the lower cooling system temperature to maintain a materialtemperature of 36° C. in the aqueous portion of the reactor as theexothermic oxidation proceeded. A flow through gas cell was used todeliver headspace gasses from the reactor to the light path of an FT-IRspectrometer allowing for in situ measurements of headspace composition.After about 4.5 hours the headspace in the non-cooled experimentconsisted of nearly 95% total NO₂ units and the reactor had to be ventedto maintain 4 barg pressure. The headspace temperature rose to 50° C. inthe non-cooled headspace due to the exothermic reaction 2 NO+O₂≈2 NO2.At the same time point in the “headspace” cooled experiment (−12° C.),the headspace consisted of only 55% total NO₂ units (See, FIG. 1) andthe reactor did not need to be vented to maintain 4 barg pressure. Theheadspace condenser was able to keep the temperature of the headspacebelow 5.5° C. despite the exothermic reaction 2 NO+O₂≈2 NO₂. This lowertemperature shifts the equilibrium of the dimerization of NO₂ to N₂O₄allowing for more N₂O₄ to form then enables N₂O₄ to condense into theliquid phase. Once in the liquid phase the N₂O₄ can react with water tomake HNO₃ and HNO₂ according to the reaction N₂O₄+H₂O≈HNO₂+HNO₃.

Example 9 NO_(x) Oxidation by Increased Agitation

1.1 grams sodium nitrite were dissolved in 1753 grams of 62.5% D-glucosesolution then the mixture was loaded into a 6 liter glass reactor. Thereactor contained a cooling jacket that was used to maintain the glucosemixture at 15° C. 1,110 grams of 69% nitric acid was added to themixture and the reactor was pressurized with 1 barg of oxygen. Themixture was then allowed to react for 6 hours continually adjusting thejacket temperature to maintain a material temperature of 35° C. in thereactor as the exothermic oxidation proceeded. The reaction was agitatedusing an overhead stir motor attached to an agitation shaft with apaddle type agitator in the liquid space of the reactor, the motor wasrun at 300 RPM. A flow through gas cell was used to deliver headspacegasses from the reactor to the light path of an FT-IR spectrometerallowing for in situ measurements of headspace composition. During thecourse of the 7 hour oxidation the composition of NO₂ in the headspacereached a maximum of 56% then slowly diminished to a about 46% as thereaction subsided. The liquid material turned dark green in colorindicating the presence of dissolved nitrogen oxide species and theheadspace had turned dark brown in color due to the high concentrationof NO₂ gas. At this time the jacket was used to cool the material to 7°C. and the agitation was increased to 475 RPM and the material wasmaintained at these conditions for an additional 17 hours. The decreasedtemperature effectively quenched the oxidation, which ceased theproduction of any new NO_(x) species, and the increased agitationresulted in a larger surface area at the gas-liquid boundary which drovethe equilibria of headspace chemistries allowing for effective oxidationof NO_(x) back to HNO₃. At the end of the 17 hours, the readspacecomposition was again measured using the flow through FT-IR cell and thetotal NO₂ composition was found to be less than 0.25% and both theliquid and the headspace were colorless.

Example 10 NO_(x) Oxidation by Circulation

1.70 grams sodium nitrite were dissolved in 2,716 grams of 62.5%D-glucose solution and the resulting mixture was loaded into a 7 literstainless steel reactor. The reactor had separate cooling jackets andseparate internal cooling coils for the top and bottom halves allowingfor separate temperature zones in the headspace and the aqueous space ofthe reactor. The headspace and aqueous space were agitated using anoverhead stirring motor attached to an agitation shaft with 1 impellerin the aqueous space and three impellers in the headspace. The lowercooling system was used to maintain the glucose mixture at 20° C. 1,720grams of 69% nitric acid was added to the mixture, the reactor waspressurized with 4 barg of oxygen, and the upper cooling system wasadjusted to provide a surface temperature of −12° C. in the headspaceportion of the reactor. The mixture was allowed to react for 6 hourscontinually adjusting the lower cooling system temperature to maintain amaterial temperature of 36° C. in the aqueous portion of the reactor asthe exothermic oxidation proceeded. After about 45 minutes, the aqueousmaterial turned from a colorless solution to a dark green solutionindicating the presence of dissolved NO₂ and aqueous N₂O₃ in themixture. As the nitric acid was reduced to nitric oxide gas, the nitricoxide quickly reacted with the oxygen in the headspace and producedbrown NO₂ gas. A flow through gas cell was used to deliver headspacegasses from the reactor to the light path of an FT-IR spectrometerallowing for in situ measurements of headspace composition. After thecompletion of the 6 hour oxidation period 334 mmoles of NO2 weremeasured in the headspace portion of the reactor. A sample of the liquidmaterial was taken and analyzed for composition using Ion chromatographyand mass spectrometry. These methods indicated the existence of 2.62moles of nitrous acid and 969.2 moles of nitric acid in the mixture.Then the lower cooling system was used to reduce the temperature of thematerial in the aqueous space of the reactor to 20° C. effectivelyquenching the oxidation reaction and ceasing the production of any newNO_(x) species. A recirculation pump was turned on and the liquidmaterial was sprayed into the headspace of the reactor at a rate of 1liter per minute. The use of a recirculating spray increased the surfacearea between the liquid and gas phases removing the mass transferlimitations resulting in a dramatic reduction in both NO₂ in the reactorheadspace and N₂O₃ in the reactor liquid space. This resulted in boththe liquid and the gas phases returning to a (normal) colorless state.After the recirculation period, the flow through FT-IR cell was used tomeasure 137 mmoles of NO₂ in the reactor headspace (a 59% decrease inNO₂). Another liquid sample was taken and the ion chromatography andmass spectrometry analysis of this sample indicated the existence of0.57 moles of nitrous acid (a 78.4% decrease) and 21.30 moles of nitricacid (a 36.2% increase).

Example 11 NOx Oxidation by Circulation, Quantification of Dissolved NOxSpecies

1.1 grams sodium nitrite were dissolved in 1,753 grams of 62.5%D-glucose solution then the mixture was loaded into a 6 liter glassreactor. The reactor had a cooling jacket that could be used to maintaina constant material temperature inside the reactor during an exothermicreaction. This jacket was used to maintain the glucose mixture at 35° C.1,110 grams of 69% nitric acid was added to the mixture, the reactor waspressurized with 1 barg of oxygen, and the mixture was allowed to reactfor 6 hours continually adjusting the jacket temperature to maintain amaterial temperature of 35° C. in the reactor as the exothermicoxidation proceeded. The reaction was kept well mixed using an overheadstir motor attached to an agitation shaft with a paddle type agitator inthe liquid space of the reactor. The headspace of the reactor was cooledusing a cooling coil with recirculating ethylene glycol chilled to −5°C. A flow through gas cell was used to deliver headspace gasses from thereactor to the light path of an FT-IR spectrometer allowing for in situmeasurements of headspace composition. During the course of the 7 houroxidation NO₂ began to build in the headspace of the reactor turning theheadspace brown in color. The liquid material had turned dark green incolor indicating the presence of dissolved nitrogen oxide species andthe headspace had turned dark brown in color due to the highconcentration of NO₂ gas. At this time the gas from the reactor wasvented and the amount of dissolved nitrogen oxide species was quantifiedas follows.

The dark green material was transferred to a suitable vacuum vessel andde-gassed under reduced pressure with agitation. The outlet of thevacuum pump was attached to a flow meter and a flow through FT-IR cellso that both the flow rate and the composition of the gas removed fromthe liquid material could be measured. After about 10 minutes, the darkgreen liquid material had turned colorless and no more gas was beingremoved from the liquid as indicated by the flow meter reading zero. Theloss of color was due to the disassociation of green N₂O₃ (l) to formone mole each of NO₂ (g) and NO (g). The data obtained from the flowmeter and the FT-IR analysis was used to calculate the number of molesof NO₂ equivalents that was dissolved in the liquid with the followingformula:

$n = {\sum\frac{1\mspace{14mu}{atm}*F_{i}}{R*20\mspace{14mu}{sk}}}$where n is number of moles, F_(i) is the flow rate for the i^(th)measurement in cm³, 293 K is the average temperature in kelvin and R isthe ideal gas constant 82.05 cm³/min atm K⁻¹ mole⁻¹. Each of N₂O₃ andN₂O₄ were treated as two NO₂ equivalents while each of NO₂ and NO weretreated as one NO₂ equivalent in this analysis. Using this method,approximately 1395 mmoles of NO₂ equivalents were measured.

Next, an identical oxidation was performed except this time at the endof the 7 hour oxidation the material was cooled to 8.5° C. effectivelyquenching the oxidation and ceasing the production of any new NOxspecies. Simultaneously, a recirculation pump was turned on and theliquid material was sprayed into the headspace of the reactor at a rateof 2 liters per minute. The use of a recirculating spray increased thesurface area between the liquid and gas phases facilitating theoxidation of NO_(x) to nitric acid resulting in a dramatic reduction inboth NO₂ in the reactor headspace and dissolved NO_(x) in the liquidspace. The material was circulated in this manner for 90 min after whichthe same method was used to quantify the amount of dissolved NO₂equivalents in the liquid. This time only 84 mmoles of dissolved NO₂equivalents were measured (a 94% reduction from the non-circulatedoxidation).

It is understood that the foregoing examples are merely illustrative ofthe present invention. Certain modifications of the articles and/ormethods may be made and still achieve the objectives of the invention.Such modifications are contemplated as within the scope of the claimedinvention.

What is claimed is:
 1. A method of synthesizing a mixture of organicacids, the method comprising the steps of: (a) combining, over time, inone or more closed reaction vessels, under a positive pressure of oxygenand with continuous mixing, an organic compound and an aqueous solutionof nitric acid to form a first reaction mixture, wherein the organiccompound and the aqueous solution of nitric acid are introduced into theone or more closed reaction vessels; (b) flowing said first reactionmixture through the one or more closed reaction vessels whilemaintaining (i) a controlled temperature of from about 5° C. to about105° C. in a portion of the reaction vessel, (ii) a reaction vesselheadspace temperature of from about 80° C. to about −42° C., and (iii) acontrolled positive pressure of oxygen of from about 0 barg to about1000 barg, to form a subsequent reaction mixture comprising a mixture oforganic acid products and nitrogen oxides, wherein the reaction vesselheadspace is maintained at a lower temperature than the temperature ofthe liquid phase; (c) recirculating the subsequent reaction mixture tothe reaction vessel vapor space headspace until the nitric acidoxidation is quenched; and (d) recovering nitric acid from thesubsequent reaction mixture, wherein the organic compound is selectedfrom the group consisting of monohydric alcohols, diols, polyols,aldehydes, ketones, carbohydrates, hydroxyacids, cellulose, starch andcombinations thereof.
 2. The method of claim 1, wherein the one or moreclosed reaction vessels comprises one or more reactors.
 3. The method ofclaim 2, wherein the one or more closed reaction vessels are in series(continuous) or in parallel with one another (batch).
 4. The method ofclaim 2, wherein the reactor is a continuously stirred tank reactor(CSTRs) or a tubular type plug flow reactor.
 5. The method of claim 1,wherein the method is a continuous process.
 6. The method of claim 1,wherein the method is a batch process.
 7. The method of claim 1, whereinthe organic compound comprises a single organic material or a mixture oforganic materials.
 8. The method of claim 1, further comprising the stepof removing a significant portion of the nitric acid from the subsequentreaction mixture.
 9. The method of claim 8, wherein the removal of thenitric acid is accomplished by an evaporation, distillation,nanofiltration, diffusion dialysis or alcohol or ether precipitation.10. The method of claim 8, further comprising the step of making basicthe subsequent reaction mixture from which most of the nitric acid hasbeen removed to convert residual nitric acid to inorganic nitrate andthe mixture of organic acids to a mixture of organic acid salts.
 11. Themethod of claim 1, wherein the carbohydrates are selected from the groupconsisting of monosaccharides, disaccharides, oligosaccharides, aldonicacids, aldonic acid esters, aldonic acid salts, aluronic acids,alduronic acid esters, alduronic acid salts, alditols, cyclitols, cornsyrups with different dextrose equivalent values, and monosaccharides,disaccharides, oligosaccharides and polysaccharides derived from plants,microorganisms or biomass sources.
 12. The method of claim 1, whereinthe nitrogen oxides are N₂O₃, N₂O₄, NO, NO₂ and N₂O.